Feedback control by RF waveform tailoring for ion energy distribution

ABSTRACT

A system for controlling RF power supplies applying power to a load, such as a plasma chamber, includes a master power supply and a slave power supply. The master power supply provides a control signal, such as a frequency and phase signal, to the slave power supply. The slave power supply receives the frequency and phase signal and also receives signals characteristic of the spectral emissions detected from the load. The slave RF power supply varies the phase and power of its RF output signal applied to the load. Varying the power controls the width of an ion distribution function, and varying the phase controls a peak of the ion distribution. Depending upon the coupling between the RF generators and the load, different spectral emissions are detected, including first harmonics, second harmonics, and, in the case of a dual frequency drive system, intermodulation distortion.

FIELD

The present disclosure relates to RF generator systems and to RFgenerator control systems.

BACKGROUND

The background description provided here is for the purpose of generallypresenting the context of the disclosure. Work of the presently namedinventors, to the extent it is described in this background section, aswell as aspects of the description that may not otherwise qualify asprior art at the time of filing, are neither expressly nor impliedlyadmitted as prior art against the present disclosure.

Plasma etching is frequently used in semiconductor fabrication. Inplasma etching, ions are accelerated by an electric field to etchexposed surfaces on a substrate. The electric field is generated basedon RF power signals generated by a radio frequency (RF) generator of aRF power system. The RF power signals generated by the RF generator mustbe precisely controlled to effectively execute plasma etching.

A RF power system may include a RF generator, a matching network, and aload (e.g., a plasma chamber). The RF generator generates RF powersignals, which are received at the matching network. The matchingnetwork matches an input impedance of the matching network to acharacteristic impedance of a transmission line between the RF generatorand the matching network. This impedance matching aids in maximizing anamount of power forwarded to the matching network (“forward power”) andminimizing an amount of power reflected back from the matching networkto the RF generator (“reverse power”). Forward power may be maximizedand reverse power may be minimized when the input impedance of thematching network matches the characteristic impedance of thetransmission line.

In the RF power source or supply field, there are typically twoapproaches to applying the RF signal to the load. A first, moretraditional approach is to apply a continuous wave signal to the load.In a continuous wave mode, the continuous wave signal is typically asinusoidal wave that is output continuously by the power source to theload. In the continuous wave approach, the RF signal assumes asinusoidal output, and the amplitude and/or frequency of the sinusoidalwave can be varied in order to vary the output power applied to theload.

A second approach to applying the RF signal to the load involves pulsingthe RF signal, rather than applying a continuous wave signal to theload. In a pulse mode of operation, a RF sinusoidal signal is modulatedby a modulation signal in order to define an envelope for the modulatedsinusoidal signal. In a conventional pulse modulation scheme, the RFsinusoidal signal typically is output at a constant frequency andamplitude. Power delivered to the load is varied by varying themodulation signal, rather than varying the sinusoidal, RF signal.

In a typical RF power supply configuration, output power applied to theload is determined by using sensors that measure the forward andreflected power or the voltage and current of the RF signal applied tothe load. Either set of these signals is analyzed in a typical controlloop. The analysis typically determines a power value which is used toadjust the output of the RF power supply in order to vary the powerapplied to the load. In a RF power delivery system, where the load is aplasma chamber, the varying impedance of the load causes a correspondingvarying power applied to the load, as applied power is in part afunction of the impedance of the load.

In plasma systems, power is typically delivered in one of twoconfigurations. In a first configuration, the power is capacitivelycoupled to the plasma chamber. Such systems are referred to ascapacitively coupled plasma (CCP) systems. In a second configuration,the power is inductively coupled to the plasma chamber. Such systems aretypically referred to as inductively coupled plasma (ICP) systems.Plasma delivery systems typically include a bias power and a sourcepower applied to one or a plurality of electrodes. The source powertypically generates the plasma, and the bias power tunes the plasma toan energy relative to the bias RF power supply. The bias and the sourcemay share the same electrode or may use separate electrodes, inaccordance with various design considerations.

When a RF power delivery system drives a load in the form of a plasmachamber, the electric field generated by the power delivered to theplasma chamber results in ion energy within the chamber. Onecharacteristic measure of ion energy is the ion energy distributionfunction (IEDF). The ion energy distribution function (IEDF) can becontrolled with a RF waveform. One way of controlling the IEDF for asystem in which multiple RF power signals are applied to the load occursby varying multiple RF signals that are related by frequency and phase.The frequencies between the multiple RF power signals are locked, andthe relative phase between the multiple RF signals is also locked.Examples of such systems can be found with reference to U.S. Pat. Nos.7,602,127, 8,110,991, and 8,395,322, assigned to the assignee of thepresent invention and incorporated by reference in this application.

RF plasma processing systems include components for plasma generationand control. One such component is referred to as a plasma chamber orreactor. A typical plasma chamber or reactor utilized in RF plasmaprocessing systems, such as by way of example, for thin-filmmanufacturing, utilizes a dual frequency system. One frequency (thesource) of the dual frequency system controls the generation of theplasma, and the other frequency (the bias) of the dual frequency systemcontrols ion energy. Examples of dual frequency systems include systemsthat are described in U.S. Pat. Nos. 7,602,127; 8,110,991; and 8,395,322referenced above. The dual frequency system described in theabove-referenced patents requires a closed-loop control system to adaptRF power supply operation for the purpose of controlling ion density andits corresponding ion energy distribution function (IEDF).

Multiple approaches exist for controlling a plasma chamber forgenerating plasmas. For example, phase and frequency of the driving RFsignals may be used to control plasma generation. For RF driven plasmasources, the periodic waveform effecting plasma sheath dynamics and thecorresponding ion energy is generally known and the frequency of theperiodic waveforms and the associated phase interaction. Anotherapproach involves dual frequency operation. That is two RF frequencysources are used to power a plasma chamber to provide substantiallyindependent control of ion and electron densities.

Another approach utilizes wideband RF power sources to drive a plasmachamber, but includes certain difficulties. One difficulty is couplingthe power to the electrode. A second difficulty involves that thetransfer function of the generated waveform to the actual sheath voltagefor a desired IEDF must be formulated for a wide-process space tosupport material surface interaction. In yet another approach, in aninductively coupled plasma approach, controlling power applied to asource electrode controls the plasma density while controlling powerapplied to the bias electrode controls the IEDF to provide etch ratecontrol. By using source electrode and bias electrode control, the etchrate is controlled via the ion density and energy.

While the above systems enable a certain degree of control of a plasmaprocess, the continually increasing need for smaller components andincreased yields demand continual improvement over the above-describedapproaches.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

A radio frequency (RF) generator system includes a power source thatgenerates a RF output signal applied to a load. A sensor detectsspectral emissions from the load, where the spectral emissions includeat least one of harmonics and intermodulation distortion (IMD). Acontrol module varies the output signal in accordance with one of theharmonics or the IMD detected in the spectral emissions.

A radio frequency (RF) power delivery system includes a first powersupply that generates a first RF output signal and a second power supplythat generates a second RF output signal. A sensor detects spectralemissions from a load, where the spectral emissions include at least oneof a harmonic of the first or second power supply and intermodulationdistortion (IMD) between the first RF signal and the second RF signal. Acontroller varies the second RF output signal in accordance with atleast one of a control signal from the first power supply, or at leastone of the harmonic or the IMD.

A radio frequency (RF) system includes a first RF generator having afirst power source, where the first RF generator generates a controlsignal. A second RF generator includes a second power source, where thesecond RF generator receives the control signal from the first RFgenerator. The control signal includes phase and frequency information.The second RF generator has a signal processing unit, and generates thesignal processing unit generating at least one of a phase or a powercommand applied to the second power source.

A controller for a RF power supply system includes aharmonic/intermodulation distortion (IMD) processor. The IMD processorreceives a frequency input signal and spectral emissions sensed from aload, and the harmonic/IMD processor generates a phase setting. A phasedetermination processor receives at least one of the frequency inputsignal, the phase setting, or a sensor signal characteristic of a powerapplied to the load. The phase determination processor generates a phasecontrol signal in accordance with the received signals.

A method for controlling a radio frequency (RF) generator includesdetecting spectral emissions from a load, where the spectral emissionshave at least one a harmonic and intermodulation distortion (IMD). Anoutput signal of a RF power source is varied in accordance with one ofthe harmonic or the IMD detected in the spectral emissions.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings. The drawingsdescribed herein are for illustrative purposes only of selectedembodiments and not all possible implementations, and are not intendedto limit the scope of the present disclosure.

FIG. 1 depicts a representation of an inductively coupled plasma system;

FIG. 2 depicts a representation of a capacitively coupled plasma system;

FIG. 3 depicts a generalized representation of a plasma system arrangedaccording to various embodiments of the present disclosure;

FIG. 4 depicts waveforms of the plasma sheath voltage and the ionapparent voltage relating to time for a particular implementation of theplasma system of FIG. 3;

FIG. 5 depicts a two-dimensional plot of ion voltage versus normalizedphase for a particular implementation of the plasma system of FIG. 3;

FIG. 6 depicts a three-dimensional plot of ion voltage versus normalizedphase versus ion energy distribution for a particular implementation ofthe plasma system of FIG. 3;

FIG. 7 depicts a plot of normalized phase versus sheath voltageemissions at a base frequency and a second harmonic of the basefrequency for a particular implementation of the plasma system of FIG.3;

FIG. 8 depicts a plot of normalized phase versus a harmonic voltagemeasured at two different locations in a plasma drive system for aparticular implementation of the plasma system of FIG. 3;

FIG. 9 depicts a three-dimensional plot of ion voltage versus normalizedphase versus ion energy distribution for a particular implementation ofthe plasma system of FIG. 3;

FIG. 10 depicts a plot of normalized phase versus sheath voltageemissions for a harmonic and intermodulation distortion frequency of abase drive signal for a particular implementation of the plasma systemof FIG. 3;

FIG. 11 depicts a block diagram of a RF control system arrangedaccording to the principles of the present disclosure;

FIG. 12 is a representation an ICP system showing interconnectionsbetween the RF generators and sensors according to the presentdisclosure;

FIG. 13 is a block diagram of a RF control system of the presentdisclosure implemented on a CCP system; and

FIG. 14 is flow diagram of a method for tailoring an RF waveform for ionenergy distribution.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

FIG. 1 depicts an exemplary representation of an inductively coupledplasma (ICP) system 10. ICP system 10 includes a plasma chamber 12 forgenerating plasma 14. Power in the form of voltage or current is appliedto plasma chamber 12 via a pair of coils, including an inner coil 16 andan outer coil 18. Power is applied to inner coil 16 via a RF powersource 20, and power is applied to outer coil 18 via a RF generator orpower source 22. Coils 16 and 18 are mounted to a dielectric window 24that assists in coupling power to plasma chamber 12. A substrate 26 isplaced in plasma chamber 12 and typically forms the work piece that isthe subject of plasma operations. A RF generator or power source 28applies power to plasma chamber 12 via substrate 26. In variousconfigurations, the RF power sources 20, 22 provide a bias voltage orcurrent to ignite or generate plasma 14. Also in various configurations,RF power supply 28 provides a bias voltage or current that varies theion energy and/or ion density of the plasma 14. In variousconfigurations, RF sources 20, 22, and 28 are locked to operate at thesame frequency, voltage, and current, with fixed or varying relativephases. In various other configurations, RF sources 20, 22, and 28 mayoperate at different frequencies, voltages, and currents, and relativephases.

FIG. 2 depicts an exemplary representation of a capacitively coupledplasma (CCP) system 30. CCP system 30 includes a plasma chamber 32 forgenerating plasma 34. A pair of electrodes 36, 38 placed within plasmachamber 32 connect to respective RF generators or power sources 40, 42.In various configurations, RF power source 40 provides a source voltageor current to ignite or generate plasma 34. Also in variousconfigurations, RF power source 42 provides a bias voltage or currentthat varies the ion energy and/or ion density of the plasma 34. Invarious configurations, power sources 40, 42 operate at the samefrequencies, voltages, and currents, and relative phases. In variousother configurations, power supplies 40, 42 operate at differentfrequencies, voltages, and currents, with fixed or varying relativephases. Also in various configurations, power supplies 40, 42 can beconnected to the same electrode, while the other electrode is connectedto ground or to yet a third RF generator.

FIG. 3 depicts a generalized representation of a dual frequency plasmasystem 50 and will be used to describe general operation of the RF powersystem of the present disclosure. Plasma system 50 includes a firstelectrode 52 connected to a ground 54 and a second electrode 56 spacedapart from first electrode 52. A low frequency first power source 58generates a first RF power applied to second electrode 56 at a firstfrequency f. A high-frequency second power source 60 generates a secondRF power applied to second electrode 56 at a second frequency nω that isthe n^(th) harmonic frequency of the frequency of first power source 58.

Application of the respective first and second powers to secondelectrode 56 generates plasma 62 having an electron density n_(e).Within the plasma 62 is a sheath layer which has a greater density ofpositive ions, and, thus, an overall excess positive charge thatbalances an opposite negative charge on the surface of a material withinthe plasma (not shown) with which it is in contact. Determining theposition of the sheath is relevant to the plasma processing operation.The position of the sheath relative to first electrode 52 and secondelectrode 56 can be defined in accordance with the sheath modulationfunction shown in equation (1):s(t)=Σ_(∀n)(s _(n) +s _(n) sin(n2πft+θ _(n)))   (1)where:

-   -   ω=2πf is the lower frequency f of the dual frequency system; and    -   θ_(η) is the relative phase between the frequencies, in this        case for harmonic tones (n>1).        The term s_(n) is the amplitude of the sheath oscillation and is        defined in equation (2):

$\begin{matrix}{s_{n} = {\frac{I_{n}}{{en}_{e}n\;\omega\; A}{\forall n}}} & (2)\end{matrix}$where:

-   -   I_(n) is the drive current associated with ω_(n);    -   n_(e) is the electron density;    -   A is the electro discharge area; and    -   e is electron charge.

The above equations (1) and (2) demonstrate that the position of thesheath varies in accordance with the relative phase between θ, in thecase of equation (1), and the applied power, I_(n) in the case ofequation (2). In terms of the IEDF, the applied power I_(n) is sometimesreferred to as the relative amplitude variable or width, and therelative phase θ is sometimes referred to as the relative phase variableor skew.

A useful property characterizing the sheath can be found with respect tothe sheath voltage described below with respect to equation (3):

$\begin{matrix}{{V_{sh}(t)} = {{- \frac{{en}_{e}}{2e_{0}}}{s^{2}(t)}}} & (3)\end{matrix}$where

-   -   e₀ is the electron charge permittivity of free space, and    -   e,n_(e), and s(t) are as described above.        From the amplitude of the sheath oscillation s_(n), an ion        voltage for the plasma can be determined in accordance with        equation (4):

$\begin{matrix}{{V_{ion}(t)} = {\frac{{en}_{e}}{2e_{0}}\left\lbrack {\sum_{\forall n}\left( {s_{n} + {\alpha_{n}{\sin\left( {{n\; 2\pi\;{ft}} + \theta_{n}} \right)}}} \right)} \right\rbrack}} & (4)\end{matrix}$where:

-   -   s_(n), e,n_(e),e₀,n,f, and θ are described above; and

$\begin{matrix}{\alpha_{n} = \frac{s_{n}}{n\;{\omega\tau}_{i}}} & (5)\end{matrix}$where:

-   -   s_(n),n, and ω are described above; and

$\begin{matrix}{\tau_{i} = {3\sqrt{\frac{m_{i}}{2\mspace{14mu}{eV}_{DC}}}}} & (6)\end{matrix}$where:

-   -   m_(i) is the mass of the ions; and    -   V_(DC) is direct current (DC) voltage that characterizes the        plasma.        FIG. 4 presents waveforms demonstrating the plasma sheath        voltage V_(sh)(t) shown at waveform 68 and the ion apparent        voltage V_(ion)(t) shown at waveform 70. The scale for the        plasma sheath voltage 68 is provided on the left y-axis, and the        scale for the ion apparent voltage 70 is provided on the right        y-axis. The x-axis provides a timescale in nanoseconds. As can        be seen from FIG. 4, the ion apparent voltage shown at waveform        70 provides an approximate envelope for the plasma sheath        voltage 68.

Driving one electrode of the pair at multiple harmonics enables thecontrol of the DC self-bias electrically by adjusting the phase betweenthe driving frequencies. Driving one electrode also enables tailoringthe shape of the IEDF by controlling higher-order moments of the IEDFand customizing the sheath voltage waveform at the substrate. To adjustto a specific IEDF, the equations above for sheath dynamics can beparticularized. For example, assuming that the plasma system 10 of FIG.3 is a dual frequency, CCP system, the sheath thickness is described asa function of time in equation (7):s(t)=s ₁(1−sin(ωt))+s ₂(1−sin(ωnt+φ))   (7)where:

-   -   ω=2πf is described above for equation (1); and    -   φ is the relative phase between the harmonic tones (n>1).        Equation (7) is a thus particular representation of equation        (1), with n=2. The amplitudes of the sheath oscillation are        defined by equation (2), above. Further, the time dependent        sheath voltage is described by equation (8):

$\begin{matrix}{{V_{bias}(t)} = {\frac{e\;\eta_{e}}{2ɛ_{0}}{s^{2}(t)}}} & (8)\end{matrix}$where the equation terms are described above with respect to equation(3). It should be noted that equations (3) and (8) are similar anddiffer with one being the negative of the other.

From the above equations, the relative phase and current magnitude arecontrollable elements of the RF power delivery system. Power setpointsadjust the corresponding I_(n) of equation (2), and the frequencies ofthe dual RF power delivery system are harmonically derived, enablingphase locking. The sheath voltage V_(bias)(t) of equation (8) isgoverned by the frequency, phase, and amplitude of the RF signal toproduce specific IEDFs from the arbitrary waveform generation with theRF power delivery scheme. In summary, (1) the sheath voltage is afunction of the driven frequencies and the power absorbed; (2) the ionvoltage is directly influenced by the sheath voltage; and (3) the sheathvoltage may control the RF power supply to influence the ion voltage andthe distribution of the ion energy.

In a particular example of the generalized description above for sheathdynamics, for an ICP source, the plasma sheath relationship between dualinductive coils and between these coils and the bias cathode benefitfrom digital phase lock loop. For an ICP systems with dual inductivecoils, the sheath thickness described in equation (1) (with n=2) isgeneralized and parameterized as a function of time as shown in equation(9)s(t)=α _(i) sin(ωt+ϕ _(i))+α _(o) sin(ωt+ϕ ₀)+s _(b) sin(ωt+ϕ _(b))  (9)where:

-   -   α_(i) and α_(o) are the amplitudes of the sheath oscillation        from the sources for the respective inner and outer coils;    -   s_(b) is the amplitude of the sheath oscillation for the bias;        and    -   ϕ is the relative phase between the RF signals applied to the        respective source and bias. For both sheath modulation        functions, the bias voltage is obtained by a squaring of the        time-varying sheath equation (9). By squaring a function of        sinusoids, harmonics components are derived. If the sinusoidal        functions comprise different frequencies, intermodulation        distortion products are also generated.

In summary, the RF power supplies connected to a plasma chamber can bevaried to control to ion energy, where the ion voltage is generated bythe squaring of the sheath modulation. As a result, harmonic emissionsfrom the ion voltages are generated. The harmonic quantities provide afeedback mechanism of the ion energy is formed.

As will be described in greater detail, the system examines the RFspectrum emitted from the sheath. From the RF spectrum, the signalcharacteristics, such as magnitude and phase, are determined from theharmonic and intermodulation distortion products to characterize thesheath voltage and the ion energies to be controlled. From the signalcharacteristics, the condition of the ion energy distribution function(IED) is determined, and the RF power delivery system is controlled toachieve a desired IEDF result. Control of the RF power delivery systemthus varies in accordance with the RF spectrum emissions.

In various embodiments described herein, one embodiment addresses aninductively coupled plasma (ICP) source example with RF power coupled atthe same frequency driven at the source and bias electrodes. In variousembodiments, capacitively coupled plasma (CCP) has a source RF powercoupled with the bias power supply to mix a set of frequencies. Invarious embodiments, the ion energy distribution function can bepositively influenced by power control and bias to source phase controldirected by feedback derived from spectral harmonic emission. In variousembodiments, a harmonically related RF power delivery system coupled toa bias electrode provides controllability of the ion energy distributionfunction from sheath voltage emissions of harmonic and intermodulationdistortion products.

FIGS. 5-8 depict plots of the sheath modulation and ion voltage as afunction of the interaction between the source RF power supplies and thebias RF power supply, such as in between RF power supplies 20, 22(considered source supplies) and RF power supply 28 (considered a biassupply) of an ICP system, such as shown in FIG. 1. In this particularexample, the frequency and phase of RF power supplies 20, 22 are locked.In this particular example, the frequency of power supplies 20, 22, 28is 13.56 MHz. Also, in this example, the phase between the RF signalsoutput by source RF power supplies 20, 22 and the bias power supply 28is varied. The current output by source RF power supplies 20, 22 is heldconstant.

FIGS. 5 and 6 depict an IEDF waveform 80 as a function of the ionvoltage and the phase, shown as normalized in the plots. FIG. 5 is atwo-dimensional representation of the IEDF plot, and FIG. 6 is athree-dimensional representation of the IEDF plot. Thus, FIG. 5 alsoshows the magnitude of the IEDF. The x-axes of FIGS. 5 and 6 representthe ion voltage in electron volts (eV), the y-axes represent the biasphase, which is normalized for the voltage applied to the bias, and thez-axes represent the IEDF. As can be seen in FIGS. 5 and 6. with thephase between the source RF power supplies 20, 22 and the bias RF powersupplies 28 (the bias phase) near 1, there are two distinct peaks thatare noted as lower peak 82 and higher peak 84. As best seen in FIG. 6,the peaks are at the periphery of the IEDF. As the bias phase isreduced, the peaks widen, with a maximum width at an approximate biasphase of 0.2, and then begin to converge. At a bias phase ofapproximately −0.8, the lower and higher peaks meet to form amono-energetic peak 86. As the bias phase continues to reduce, thesingle peak begins to diverge back to the two individual peaks.

FIG. 7 depicts waveforms of the sheath voltage emission at a directcurrent (DC) 90, a frequency of 13.56 MHz 92, and at a frequency of27.12 MHz 94. The frequency of 27.12 MHz is a second harmonic of thefrequency of 13.56 MHz. In FIG. 7, the x-axis represents the normalizedphase, and the y-axis represents the emissions from the plasma chamber,such as plasma chamber 12 of FIG. 1. As can be seen, the 13.56 MHz and27.12 MHz voltage signals correspond to the width of the IEDF, and theminimum of these signals coincide with the mono-energetic IEDF peak 86of FIG. 6 at a phase of −0.8.

FIG. 8 depicts plots of the normalized phase along the x-axis versus theharmonic voltage measured at a matching network and plotted along theleft y-axis and the harmonic voltage measured at the RF generatorplotted along the right y-axis. Waveform 100, represented by circles,corresponds to the harmonic voltage at the matching network, andwaveform 102, represented by squares, corresponds to the harmonicvoltage at the RF generator. The harmonic voltage may be measured usingthe voltage/current probe. More specifically, the harmonic voltage atthe matching network may be measured by placing a VI probe between theoutput of the matching network and the bias electrode. Similarly, theharmonic voltage of the RF generator may be measured by placing a VIprobe between the output of the RF generator and a matching networkassociated with the bias electrode.

With the source RF power supplies 20, 22 and bias RF power supply 28frequency and phase locked, incremental variation of the bias phaseindicates that as the lower and higher peaks of the IEDF converged toform a single mono-energetic peak as shown in FIGS. 5 and 6, the secondharmonic voltages in FIG. 8 both reach a minimum. The minimum of the27.12 MHz voltage signal 94 of FIG. 7 corresponds to the minimum widthof the IEDF at an approximate phase angle of −0.8. The measured harmonicsignals at both the RF generator and the matching network agree with thephase measurement required for a mono-energetic IEDF peak.

In the RF power delivery system described above with respect to FIGS. 1and 5-8, examination of the RF spectrum enables varying control of theRF power delivery system to achieve a desired IEDF. In the system asdescribed above with respect to FIGS. 1 and 5-8 (sometimes referred toas a triplet of RF power supplies), the two peaks 82, 84 in the ionenergy distribution (IED) are controlled by varying the relative phasebetween the bias to source power supplies. Further, a mono-energetic ionenergy distribution function occurs at a particular bias-source phaserelationship. The mono-energetic condition is detected by a minimumvalue in the second harmonic emission, as indicated by waveform 94 ofFIG. 7.

The discussion above with respect to FIGS. 1 and 5-8 describes a tripletsystem. In a triplet system, the two RF power supplies and the RF biaspower supply operate at the same frequency, and the two RF source powersupplies and the RF bias power supply operate at a relative phase thatis varied. Another approach to driving the source RF power supply andthe bias RF power supply utilizes operating one of the source or bias RFpower supplies at a first frequency and operating the other of thesource or bias RF power supplies at a second frequency that is aharmonic of the first frequency. Such a configuration can be referred toas a harmonic drive plasma system and may be seen in connection withoperating a CCP plasma system 30, such as in FIG. 2. From the sheathmodulation function and the corresponding ion voltage, which is impactedby the sheath voltage, the phase adjustment can control the peak of theion energy distribution function in a harmonic drive plasma system.

By way of example and with reference to FIG. 2, RF power supply 42 maybe assigned as the bias electrode and driven at a frequency of 13.56MHz. Power source 40 of FIG. 2 may be assigned as the source electrodeand driven at a frequency of 27.12 MHz. FIG. 9 depicts an IEDF waveform110 in a three-dimensional graph, with normalized phase plotted alongone axis, ion voltage in electron volts plotted along a second axis, andion energy distribution (IED) plotted on a third axis. As can be seenfrom FIG. 9, the skew of the IEDF peak is linear with respect to therelative phase between the RF power supplies 40, 42. Further, the IEDFpeak 112 is periodic with normalized phase.

FIG. 10 depicts a plot of the voltage emission from a plasma chamber 34of FIG. 2 relative to a normalized phase. FIG. 10 depicts waveforms ofnormalized phase versus normalized sheath voltage emission at an IMDfrequency (waveform 120) and a second harmonic frequency (waveform 122).That is, the IMD is 40.68 MHz (13.56 MHz (bias power supplyfrequency)+27.12 MHz (source power supply 42 frequency)). The secondharmonic is 54.24 MHz (2×27.12 MHz). At a normalized phase of 0, thewaveforms of FIG. 10 span to a maximum and minimum as the phase varies.The maximum peaks 124, 126 of the respective voltage waveforms 120, 122are located at a normalized phase of −0.3, and the minimum peaks 128,130 of the respective voltage waveforms 120, 122 are approximatelycollocated at a normalized phase of 0.3. As it relates to the IEDF plotin FIG. 9, the voltage peaks correspond to the linear ion voltage rangeof the single IEDF peak. By knowing the peaks of the voltage emissionsof FIG. 10, the linear range of the IEDF peak of FIG. 9 is determined.With knowledge of the peak IEDF, the skew of the ion energies can becontrolled by varying the relative phase of the harmonic driven RF powerdelivery system.

Regardless of whether the drive system is a triplet drive system or aharmonic drive system, the foregoing provides the flexibility to controlthe IEDF and the IED peak from the RF spectrum emissions. In a tripletcoupled RF power delivery system, such as generally described in FIGS. 1and 5-8, determining a minimum voltage from a harmonic emission enablesconvergence to a single IEDF. For a harmonic derived RF power deliverysystem, such as generally described in FIGS. 2, 9, and 10, peaksdetected from spectrum emissions provide a linear relationship betweenthe relative phases of the RF signals to the IEDF peak. Thus, theembodiments described herein provide the ability to (1) determine thepeak of the ion energy distribution; and (2) subsequently control theion energy of the distribution peak.

FIG. 11 depicts a RF generator or power supply system 150 including apair of radio frequency (RF) generators or power supplies 152 a, 152 bfor driving a load (not shown). RF generators 152 a, 152 b can implementa master-and-slave configuration using a control signal, as will bedescribed in greater detail. RF generator 152 a is designated themaster, and RF generator 152 b is designated the slave. In variousembodiments, power (either voltage or current), frequency, and phase ofRF generator 152 b may be slaved to the frequency of RF generator 152 ausing a control signal sent from RF generator 152 a to RF generator 152b. In various embodiments, the frequency signal output by RF generator152 a can be determined in accordance with the spectral emissions samplefrom a load, such as a plasma chamber. When the control signal is absentfrom RF generator 152 a, RF generators 152 a and 152 b can operateautonomously. U.S. Pat. Nos. 7,602,127; 8,110,991; and 8,395,322;referenced above and incorporated herein, describes operation of a dualpower supply system in a master/slave relationship.

RF generators 152 a, 152 b include respective RF power sources oramplifiers 154 a, 154 b, RF sensors 156 a, 156 b, and processors,controllers, or control modules 158 a, 158 b. RF power sources 154 a,154 b generate RF power signals 163 a, 163 b output to respectivesensors 156 a, 156 b. Sensor 156 a, 156 b receive the output of sources154 a, 154 b and generate respective RF power signals f₁ and f₂ and alsooutput signals that vary in accordance with spectral emissions receivedfrom a load, such as a plasma chamber. While sensors 156 a, 156 b, areshown with respective RF generators 152 a, 152 b, it should be notedthat spectrum sampling of an RF sensor can occur externally to the RFpower generators 152 a, 152 b. Such external sensing can occur at theoutput of the RF generator, at the input of the impedance matchingdevice that is located between the RF generator and the plasma chamber,or between the output of the impedance matching circuit (including,inside the impedance matching device) and the plasma chamber.

Sensors 156 a, 156 b detect the spectral emissions from a load (notshown), such as a plasma chamber, and output signals X and Y. Sensors156 a, 156 b may include voltage, current, and/or directional couplersensors. Sensors 156 a, 156 b may detect (i) voltage V and current Ioutput from power amplifier 154 a, 154 b, and/or (ii) forward (orsource) power P_(FWD) output from respective power amplifiers 154 a, 154b and/or RF generators 150 a, 150 b and reverse (or reflected) powerP_(REV) received from a matching network or a load connected torespective sensor 156 a, 165 b. The voltage V, current I, forward powerP_(FWD), and reverse power P_(REV) may be scaled and/or filteredversions of the actual voltage, current, forward power, and reversepower associated with the respective power sources 154 a, 154 b. Sensors156 a, 156 b may be analog and/or digital sensors. In a digitalimplementation, the sensors 156 a, 156 b may include analog-to-digital(A/D) converters and signal sampling components with correspondingsampling rates. Signals X and Y can represent any of the voltage V andcurrent I or forward (or source) power P_(FWD) reverse (or reflected)power P_(REV).

Sensors 156 a, 156 b generate sensor signals X, Y, which are received byrespective controllers or power control modules 158 a, 158 b. Powercontrol modules 158 a, 158 b process the respective X, Y signals 160 a,162 a and 160 b, 162 b and generate one or a plurality of feedbackcontrol signals to respective power sources 154 a, 154 b. Poweramplifiers 154 a, 154 b adjust the RF power signal 163 a, 163 b based onthe received feedback control signal. Power control modules 158 a, 158 bmay include at least, proportional integral derivative (PID) controllersor subsets thereof and/or direct digital synthesis (DDS) component(s)and/or any of the various components described below in connection withthe term modules. In various embodiments, power control modules 158 a,158 b are first PID controllers or subsets and may include a functions,processes, processors, submodules or modules identified as D_(p)(z).D_(p)(z) is implemented in any one of the module variations describedbelow. Feedback control signals 164 a, 164 b may be drive signals andhave a DC offset or rail voltage, voltage or current magnitude, afrequency, and a phase.

Control module 158 a of RF power supply 152 a applies control functionD_(p)(z) to the received signals X, Y and generates feedback controlsignal 164 a. Feedback control signal 164 a includes both frequency andpower control components for controlling RF power source 154 a. Thus, RFpower source 154 a generates RF power signal 163 a in accordance withfrequency and power information communicated in feedback control signal164 a. The power information communicated in feedback control signal 164a can include voltage and/or current information. Control module 158 aalso generates a frequency and phase information signal 166 input tocontrol module 158 b of RF generator 152 b. Frequency and phaseinformation signal 166 includes frequency information, including thefrequency of f₁ and the phase of f₁.

In various embodiments, slave RF generator 152 b regulates the outputphase of f₂ relative to the input frequency and phase information signal166, and thus f₁ output by RF generator 152 a for a particular phase setpoint. Frequency and phase information signal 166 contains informationabout the phase and frequency of f₁. Control module 158 b of RF powersupply 152 b, in addition to receiving signals X, Y from sensor 156 balso receives frequency and phase information signal 166 from RFgenerator 152 a and a phase setpoint signal 168 and applies functions,processes, processors, submodules, or modules D_(p)(z) and D_(fϕ)(z) togenerate one or a pair of respective feedback control signals 164 b′,164 b″.

Control module 158 b includes harmonic/IMD processor or module 170 andtime division multiplexer or multiplexing module 172. Control modules158 a, 158 b, harmonic/IMD processor or module 170, and multiplexingmodule 172 are implemented in any one of the module variations describedbelow. Control module 158 b includes harmonic/IMD module 170, which iscoupled to the sensor 156 b to receive signals X, Y. Harmonic/IMD module170 also receives phase and frequency signal 166. Harmonic/IMD module170 generates a phase setting ϕ to digital control function D_(fϕ)(z).The phase setting ϕ defines a phase, and D_(fϕ)(z) determines a phaseand frequency of operation for RF power source 154 b in accordance withϕ. D_(fϕ) is implemented in any one of the module variations describedbelow. In a first mode of operation, harmonic/IMD module 170 generatesthe phase setting ϕ in accordance with the phase setpoint signal 168,which is received from an external source, such as an externalcontroller. The first mode of operation may be referred to as a bypassmode of operation and may be operational when harmonic/IMD module 170 isdisabled.

In the second mode of operation, such as when harmonic/IMD module 170 isenabled, harmonic/IMD module 170 generates the phase setting ϕ inaccordance with output signals X, Y and the information contained infrequency and phase information signal 166. Phase setting ϕ isdetermined in accordance with the sampled spectral emissions at theoutput of the RF sensor 156 b. The phase setting ϕ is thus determined inaccordance with the approaches described in connection with FIGS. 1-10.That is, a phase is determined in connection with one or both minimizinga harmonic of the source or the bias signal and the harmonic and the IMDof the source or bias signals.

The spectral emissions can be determined in either the frequency-domainor the time-domain. For frequency domain processing, the Fast FourierTransform (FFT) or wavelet transform can be applied to obtain from theRF sensor signals X, Y information from the frequency or frequencies ofinterest. For time domain processing, analog or digital forms ofheterodyning and associated filtering are suitable approaches to extracta specific frequency.

The control function D_(fϕ)(z) receives the phase setting ϕ andgenerates a frequency and phase feedback control signal 164 b″ to poweramplifier 154 b. Control function D_(fϕ)(z) also receives frequency andphase information from RF generator 152 a via frequency and phaseinformation signal 166. Control function D_(fϕ)(z) generates thefrequency and phase control signal 164 b ″ to power source 154 b to varythe skew parameter of the sheath modulation function, to thereby controlthe peak of the IEDF. D_(fϕ)(z) thus frequency and phase locks thesignal from RF power source 154 b with the signal from RF power source154 a.

Frequency and phase information signal 166 is input to time divisionmultiplexer (TDM) 172. TDM 172 multiplexes information contained withinfrequency and phase information signal 166 and signal information fromsignal Y output by sensor 156 b. In various embodiments, the signal Yinput to TDM can be either voltage or current. TDM 172 multiplexes thesignal 166 and the Y output from sensor 156 b and applies themultiplexed output to control function D_(fϕ)(z) and control functionD_(p)(z).

Control function D_(p)(z) receives the frequency and phase informationsignal 166 from RF generator 152 a and one of the X or Y signals fromsensor 165 b via TDM 172. In the embodiment of FIG. 13, TDM 172 receivesthe Y signal from sensor 156 b. Control function D_(p)(z) also receivesthe other of the signals X, Y output form sensor 156 b. Thus, controlfunction D_(p)(z) 176 of control module 158 b receives frequency andphase information signal 166, and the X, Y signals from sensor 156 b.Control function D_(p)(z) generates a power signal 164 b′ output to RFsource 154 b, in accordance with the received frequency, X, and Ysignals. RF source 154 b generates RF power signal 163 b. Controlfunction D_(p)(z) of control module 158 b thus generates a power signalto control the width parameter of the sheath oscillation amplitude and,therefore, the width of the IDEF, as described above with respect toFIGS. 1-10.

For either frequency or time-domain processing, the objective is toextract from the X, Y signals output by sensor 156 a, 156 b the signalsrelated to the sheath voltage emissions. The sheath voltage emissionsignals have known frequency details. In various embodiments, such asthe triplet power supply configuration discussed in connection withFIGS. 1 and 5-8, the second harmonic was sampled, 27.12 MHz in oneparticular example. In the case of the harmonic drive frequency schemediscussed in connection with FIGS. 2, 9, and 10, the intermodulationdistortion product (IMD), 40.68 MHz in one particular example, and thesecond harmonic, 54.24 MHz in one particular example, contain thenecessary signal details to determine information related to the peaklocation of the ion energy distribution and to enable adjusting theoperating parameters of RF power source 154 b to yield a peak at aparticular ion energy. Thus, the harmonic/IMD module 170 extracts signalinformation from the sampled RF sensor spectrum provided in signals X, Youtput by sensor 156 b as it relates to the sheath voltage emission. Invarious embodiments described above, the voltage signal at a harmonic ofone of the RF power sources 154 a, 154 b or the first orderintermodulation product (f₂-f₁) identifies the peak location of the ionenergy distribution. Once the peak location of the IEDF is determined byharmonic/IMD module 170, the IEDF peak location (the skew) can beadjusted to a desired position in the IEDF.

In various embodiments, the RF generators 152 a, 152 b of FIG. 11 may beindividually configured as described above or may be identicallyconfigured to effect examining spectral emissions and adjustingfrequency, power and phase accordingly. In a substantially similarconfiguration, RF generator 152 a may be arranged as described ingenerator 152 b. Further, in various embodiments, if configuredsimilarly, RF generator 152 b may be configured as a master in the RFgenerator configuration and output a control signal to a slave RFgenerator 152 a.

Various embodiments can include the RF power delivery system describedabove coupled to plasma chambers. FIG. 12 depicts various embodiments ofan ICP system 180 utilizing a configuration of the RF generatorsdescribed above with respect to FIG. 11 providing power to a plasmachamber 12 such as shown in the ICP system 10 of FIG. 1. In FIG. 12,similar components from FIG. 1 will be referred to using the samereference numerals, and the description of such similar components maybe augmented or distinguished as necessary. In addition to componentssimilar to that described in FIG. 1, FIG. 12 also includes a trio ofsensors 182, 184, 186. Sensors 182, 184, 186 are associated with arespective RF generator 20, 22, 28 and provide the X, Y inputs torespective RF generator 20, 22, 28.

With reference to FIGS. 11 and 12, RF generators 20, 22 operateanalogously to the master slave relationship defined in U.S. Pat. Nos.7,602,127, 8,110,991, and 8,395,322, and incorporated herein. RFgenerator 20 operates as a master RF generator for each of RF generator22 and RF generator 28. With respect to RF generator 22, RF generator 20outputs a frequency and phase signal to RF generator 22, and RFgenerator 22 operates as a slave generator in the context discussed inthe above-referenced US patents. RF generator 20 outputs a phase andfrequency information signal to RF generator 28, which operates as aslave in the context discussed with respect to FIG. 11.

In various embodiments of the ICP system 180, the bias RF generator 28is frequency and phase locked to the RF generators 20, 22, where RFpower supply 20 acts as a master for both RF generator 20 and RFgenerator 28. In the configuration of ICP system 180, the spectrumsampling occurs at the bias RF generator 28. RF generator 28 isconfigured similarly to RF generator 152 b of FIG. 11. Bias RF generator28 includes a harmonic/IMD module 170 that inspects the sampled biassignals at the respective harmonics X_(B),Y_(B) to adjust the relativephase between the bias RF generator 28 and the source RF generator 20.Adjusting the phase of RF generator 28 relative to the frequency andphase signal received from RF generator 20 provides control of the peaklocation within the ion energy distribution.

FIG. 13 depicts various embodiments of a CCP system 190 utilizing asimilar configuration the RF generators described above with respect toFIG. 2 for providing power to a plasma chamber 32 such as described inthe plasma system 30 of FIG. 2. In FIG. 13, similar components of FIG. 1will be referred to using the same reference numerals, and thedescription of such similar components may be augmented or distinguishedas necessary. RF generator 40 of FIG. 2 is implemented in aconfiguration similar to RF generator 152 a of FIG. 11, and RF powersource 42 is implemented in a configuration similar to RF generator 152b of FIG. 11.

As described above with respect FIG. 2, RF generators 40, 42 can beconnected to a common electrode, such as electrode 36, 38, and the otherof the two electrodes 36, 38 can be connected to ground or to yet athird RF generator. FIG. 13 also includes a pair of matching networks192, 194. Matching network 192 is configured as a dual matching networkthat receives frequency signals f₁ and f₂ and provides appropriateimpedance matching for each RF generator 40, 42. Dual matching network192 can be alternately implemented as individual networks, eachproviding an appropriate impedance match for each of respective RFgenerators 40, 42. CCP system 190 also includes a very high frequency(VHF) RF generator or source 196. In various embodiments, VHF RFgenerator 196 provides a RF signal to the other of the two electrodes36, 38 of plasma chamber 32. VHF RF generator 196 provides a VHF RFpower signal 198 to matching network 194. Matching network 194 providesan impedance match between VHF RF generator 196 and plasma chamber 32.In various embodiments, RF generators 40, 42 apply power to a biaselectrode, and VHF RF generator 186 provides power to a sourceelectrode. Thus, for the CCP system in FIG. 13, the bias is powered bytwo RF generators 40, 42 that are harmonically related in phase andfrequency locked using the approach discussed with respect to FIGS. 2,8, and 9

FIG. 14 depicts a flow diagram for a method of feedback control for RFwaveform tailoring for ion energy distribution 210 according to variousembodiments. At block 212, control begins and various parameters areinitialized. At block 214, a frequency of a master RF power supply isset, such as at a frequency f₁ having a phase. In various embodiments,the frequency f₁ is output to a load, such as a plasma chamber describedabove. Control next proceeds to block 216 in which a signal havingfrequency and phase information is sent to a controller for a slavepower supply. At decision block to 218, it is determined whether themaster and slave power supplies are operated at substantially the samefrequency, such as the ICP system discussed above, or at a dualfrequency, such as in the CCP system discussed above. It should be notedthat block 218 is considered optional to the extent that it is notnecessary if it has already been determined whether the master and slaveare driven at substantially the same or different frequencies. Block 218is, therefore, included to facilitate the understanding of the spectralemissions that are examined depending upon the frequencies at which themaster and slave power supplies are operated.

If the master and slave power supplies operate at substantially the samefrequency, control proceeds to block 220 in which the harmonicscontained within the spectral emissions from a load are examined and atarget phase is determined. If the master and slave power suppliesoperate at different frequencies, control proceeds to block 222 in whichthe harmonics and IMD contained within the spectral emissions from aload are examined and a target phase is determined. In variousembodiments, the target phase determines a peak in the IED. In either ofblocks 220 or 222, a target phase is determined, and control proceeds toblock 224. A block 224, the phase and frequency of the slave powersupply is set in accordance with the target phase. Control next proceedsto block 226 in which the power of the slave power supply is alsodetermined in accordance with the output from blocks 220 or 222. Invarious embodiments, the power set by the slave determines a width ofthe IED.

In various embodiments, it may be desirable to pulse the slave RFgenerator 152 b in order to vary the ion voltage. That is, while in someembodiments it may be desirable to operate at a mono-energetic peak,such as peak 86 of FIG. 5, or at a particular position along the peak112 of FIG. 9, other various plasma processes may benefit from operatingaway from the above-referenced peak. With reference to FIG. 5, operatingat peak 86 provides an ion voltage of approximately 155 eV. There aretimes in a manufacturing process when it may be desirable to have moreor less ion voltage. Ion voltage can be adjusted by operating at a phaseaway from −0.8 as shown in FIG. 5. For example, it is possible that theplasma operation would call for a less directed peak so that withreference to FIG. 5, if the phase is selected as 0.2, the ion voltagewould be a composite of approximately 128 eV and 185 eV in accordancewith the lower and upper peaks. In various embodiments, it may bedesirable to pulse the phase between a phase to provide a mono-energeticpeak 86 and a second phase that provides two peaks. In the exampledescribed above, the phase can alternate between −0.8 and 0.2.

With reference to FIG. 9, various plasma processes may benefit fromvarying the phase along a linear range of the peak 112. For example, thephase could be varied in the example of FIGS. 9 and 10 from the phaseequal to 0.3 for a peak along the line of peaks defined by referencenumber 112. By varying the phase, a range of the ion voltages can beprovided in a plasma system driven by the environment described inconnection with FIGS. 9 and 10.

One benefit of identifying and controlling the location of the peak ofthe ion energy distribution is improved system phase control. Forexample, in a dual RF power delivery system operating in a conventionalmaster-slave configuration where phase and frequency is locked withoutattention to the spectral emissions, at least three sources of systemicphase error exit. A first source exists between a control signaltransmitted from the master to the slave; a second source exists betweenthe output of the slave RF generator and the matching network to whichit connects; and a third source exists in the matching networkassociated with the slave RF generator. The ion peak density controlprovided by the phase regulation of the present disclosure collectivelyaddress all three sources of phase error. The slave RF generatorregulates the phase of the waveform output by the slave RF generatorwith respect to the phase of the frequency and phase signal input toslave RF generator.

Between the phase of the output of the slave RF power supply and theelectrode to the plasma chamber, there are several systematic phaseoffsets, as described above. For the phase offset relative to thereference frequency signal input (that is, between the output of themaster RF generator and the input to the slave RF generator), the cablecoupling the master to the slave will have a length L₁, and velocity ofpropagation V_(p1). Ignoring cable losses, the cable between the outputof the master RF generator and the input to the slave RF generator willhave a phase offset related by the transmission line parameters L₁ andV_(p1) and expressed as e^(jϕ1). At the output of the slave RF powersupply, two systemic phase offset contributors exist: (1) e^(jϕ2)characterizes the transmission line coupling the RF power from slave RFgenerator to its associated matching network, and (2) the phase ϕ_(MN)is associated with the transfer function for the matching network.Further, the power generator will have a varying phase output over thedesigned power range.

One approach to compensating for the phase offsets described above,which collectively characterize a systemic phase offset, requiresmeasuring each contributing factor and apply a calibrated phaseadjustment to the desired phase regulated at the output of slave RFgenerator. The calibrated phase adjustment must compensate for varyingelements in the system, such as ϕ_(PA) and ϕ_(MN). The variousembodiments described in the present disclosure avoid the inherentdeficiencies of such a complex approach. The various embodiments of thepresent disclosure rely upon the spectral emissions of the RF harmonicparameter to compensate for systemic phase offsets. That is, relyingupon the measured voltage from one or both of a harmonic orintermodulation distortion product from the sampled RF spectrum adjustsfor systemic phase offsets.

The embodiments described herein disclose that sampling the spectralemissions from a plasma chamber enable direct control of the ion energyand the corresponding ion energy distribution. In some systems, it maybe possible to measure plasma parameters contained in the spectralemissions using various sensors and instrumentation, including hairpinresonators, energy grid analyzers, and optical emission spectroscopy.From the output of these sensors, a correlation can be developed todetermine the ion energy peak distribution in accordance with settingparameters controlling the RF power delivery system. Instrumentationsuch as hairpin resonators, energy grid analyzers, and optical emissionspectroscopy, however, disrupt the plasma processing within the plasmachamber and have limited utility in a high-volume, manufacturingenvironment. In contrast, the various embodiments described in thisdisclosure result from less disruptive RF power sampling to achieve aself-contained RF power delivery system solution.

Therefore, by adjusting the RF waveform in accordance with spectralemissions from the plasma chamber, a narrow IEDF can be provided,meeting various industry requirements. In general, lower excitationfrequencies generated at a bias power supply result in higher ionenergy. Higher ion energy in turn provides improved etch rates. However,while lower frequencies provide higher ion energies, the distribution ofthe ions is considerably wider. Typically, it is desirable to have allion energies grouped into a single peak (such as the mono-energetic peakdiscussed above) versus two broad peaks. For example, ion energy at15-30 eV can damage material in the 1-2 nm range. When a singlefrequency drives the bias electrodes, each peak provides two differentmaterial removal rates. With two different material removal rates, theetch rate improvement gained by the lower frequency and increased powerat best only yields an average etch rate from the two peaks. To obtainimproved surface material removal fidelity, it is desirable to form anion energy distribution for a constant material removal rate. Thevarious embodiments discussed in the present disclosure provide a singlepeak, mono-energetic group of ions for the same etch rate with constantmaterial rate. The improved etch rates also provide improvedselectivity.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. It should be understood thatone or more steps within a method may be executed in different order (orconcurrently) without altering the principles of the present disclosure.Further, although each of the embodiments is described above as havingcertain features, any one or more of those features described withrespect to any embodiment of the disclosure can be implemented in and/orcombined with features of any of the other embodiments, even if thatcombination is not explicitly described. In other words, the describedembodiments are not mutually exclusive, and permutations of one or moreembodiments with one another remain within the scope of this disclosure.

Spatial and functional relationships between elements (for example,between modules, circuit elements, semiconductor layers, etc.) aredescribed using various terms, including “connected,” “engaged,”“coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and“disposed.” Unless explicitly described as being “direct,” when arelationship between first and second elements is described in the abovedisclosure, that relationship can be a direct relationship where noother intervening elements are present between the first and secondelements, but can also be an indirect relationship where one or moreintervening elements are present (either spatially or functionally)between the first and second elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A OR BOR C), using a non-exclusive logical OR, and should not be construed tomean “at least one of A, at least one of B, and at least one of C.”

In this application, including the definitions below, the term ‘module’or the term ‘controller’ may be replaced with the term ‘circuit.’ Theterm ‘module’ may refer to, be part of, or include: an ApplicationSpecific Integrated Circuit (ASIC); a digital, analog, or mixedanalog/digital discrete circuit; a digital, analog, or mixedanalog/digital integrated circuit; a combinational logic circuit; afield programmable gate array (FPGA); a processor circuit (shared,dedicated, or group) that executes code; a memory circuit (shared,dedicated, or group) that stores code executed by the processor circuit;other suitable hardware components that provide the describedfunctionality; or a combination of some or all of the above, such as ina system-on-chip.

The module may include one or more interface circuits. In some examples,the interface circuits may include wired or wireless interfaces that areconnected to a local area network (LAN), the Internet, a wide areanetwork (WAN), or combinations thereof. The functionality of any givenmodule of the present disclosure may be distributed among multiplemodules that are connected via interface circuits. For example, multiplemodules may allow load balancing. In a further example, a server (alsoknown as remote, or cloud) module may accomplish some functionality onbehalf of a client module.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. The term shared processor circuitencompasses a single processor circuit that executes some or all codefrom multiple modules. The term group processor circuit encompasses aprocessor circuit that, in combination with additional processorcircuits, executes some or all code from one or more modules. Referencesto multiple processor circuits encompass multiple processor circuits ondiscrete dies, multiple processor circuits on a single die, multiplecores of a single processor circuit, multiple threads of a singleprocessor circuit, or a combination of the above. The term shared memorycircuit encompasses a single memory circuit that stores some or all codefrom multiple modules. The term group memory circuit encompasses amemory circuit that, in combination with additional memories, storessome or all code from one or more modules.

The term memory circuit is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium may therefore be considered tangible and non-transitory.Non-limiting examples of a non-transitory, tangible computer-readablemedium are nonvolatile memory circuits (such as a flash memory circuit,an erasable programmable read-only memory circuit, or a mask read-onlymemory circuit), volatile memory circuits (such as a static randomaccess memory circuit or a dynamic random access memory circuit),magnetic storage media (such as an analog or digital magnetic tape or ahard disk drive), and optical storage media (such as a CD, a DVD, or aBlu-ray Disc).

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks andflowchart elements described above serve as software specifications,which can be translated into the computer programs by the routine workof a skilled technician or programmer.

The computer programs include processor-executable instructions that arestored on at least one non-transitory, tangible computer-readablemedium. The computer programs may also include or rely on stored data.The computer programs may encompass a basic input/output system (BIOS)that interacts with hardware of the special purpose computer, devicedrivers that interact with particular devices of the special purposecomputer, one or more operating systems, user applications, backgroundservices, background applications, etc.

The computer programs may include: (i) descriptive text to be parsed,such as HTML (hypertext markup language) or XML (extensible markuplanguage), (ii) assembly code, (iii) object code generated from sourcecode by a compiler, (iv) source code for execution by an interpreter,(v) source code for compilation and execution by a just-in-timecompiler, etc. As examples only, source code may be written using syntaxfrom languages including C, C++, C#, Objective C, Haskell, Go, SQL, R,Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5,Ada, ASP (active server pages), PHP, Scala, Eiffel, Smalltalk, Erlang,Ruby, Flash®, Visual Basic®, Lua, and Python®.

None of the elements recited in the claims are intended to be ameans-plus-function element within the meaning of 35 U.S.C. § 112(f)unless an element is expressly recited using the phrase “means for,” orin the case of a method claim using the phrases “operation for” or “stepfor.”

What is claimed is:
 1. A radio frequency (RF) generator systemcomprising: a power source that generates an RF output signal applied toa load; a sensor that detects spectral emissions from the load, thespectral emissions including at least one of harmonics andintermodulation distortion (IMD); and a control module that varies aparameter of the RF output signal in accordance with one of theharmonics or the IMD detected in the spectral emissions, wherein theparameter is one of phase, frequency, or amplitude.
 2. The RF generatorsystem of claim 1 wherein the control module adjusts one of a current ora voltage of the RF signal to vary a width of an ion energy distribution(IED) or a phase of the RF signal to vary a peak of the IED.
 3. The RFgenerator system of claim 1 wherein the load is an inductively coupledplasma (ICP) system.
 4. The RF generator system of claim 3 wherein, thecontrol module varies the RF output signal in accordance with a selectedharmonic detected in the spectral emissions.
 5. The RF generator systemof claim 4 wherein the control module varies a current or a voltage ofthe RF output signal in order to control a width of an ion energydistribution (IED) or a phase of the RF signal to vary a peak of theIED.
 6. The RF generator system of claim 1 wherein in a CCP system, thecontrol module varies the RF output signal in accordance with a selectedharmonic and a selected IMD detected in the spectral emissions.
 7. TheRF generator system of claim 6 wherein the control module varies acurrent or a voltage in the RF output signal in order to control a widthof an ion energy distribution (IED) or a phase of the RF signal to varya peak of the IED.
 8. The RF generator system of claim 1 wherein thesensor is disposed in one of at an input to a matching network, at anoutput of a matching network, or within a RF generator.
 9. The RFgenerator system of claim 1 wherein the load is a capacitively coupledplasma (CCP) system.
 10. The RF generator system of claim 9 wherein thecontrol module varies a current or a voltage of the RF output signal inorder to control a width of an ion energy distribution (IED) or a phaseof the RF output signal to vary a peak of the IED.
 11. The RF generatorsystem of claim 1 wherein in a CCP system, the control module varies theoutput signal in accordance with a selected harmonic and a selected IMDdetected in the spectral emissions.
 12. A method for controlling a radiofrequency (RF) generator comprising: detecting spectral emissions from aload, the spectral emissions including at least one a harmonic andintermodulation distortion (IMD); and varying a parameter of an RFoutput signal of a RF power source in accordance with one of theharmonic or the IMD detected in the spectral emissions, wherein theparameter is one of phase, frequency, or amplitude.
 13. The method ofclaim 12 further comprising adjusting one of a current or a voltage ofthe RF output signal to vary a width of an ion energy distribution (IED)or a phase of the output signal to vary a peak of the IED.
 14. Themethod of claim 12 further comprising applying the RF output signal to aload in an inductively coupled plasma (ICP) system.
 15. The method ofclaim 14 wherein in an ICP system, varying the RF output signal inaccordance with at least one selected harmonic detected in the spectralemissions.
 16. The method of claim 15 further comprising varying acurrent or a voltage of the RF output signal in order to control a widthof an ion electron distribution (IED) or a phase of the RF signal tovary a peak of the IED.
 17. The method of claim 14 wherein in a CCPsystem varying the RF output signal in accordance with a selectedharmonic and a selected IMD detected in the spectral emissions.
 18. Themethod of claim 17 further comprising varying a current or a voltage inthe RF output signal in order to control a width of an ion energydistribution (IED) or a phase of the RF signal to vary a peak of theIED.
 19. The method of claim 12 further comprising sensing at an inputto a matching network, at an output of a matching network, or within anRF generator.
 20. The RF generator system of claim 12 wherein the loadis a capacitively coupled plasma (CCP) system.
 21. The method of claim12 further comprising applying the output signal to a load in acapacitively coupled plasma (CCP) system.
 22. A radio frequency (RF)generator system comprising: a power source that generates an RF outputsignal applied to a load; a sensor that detects spectral emissions fromthe load, the sensor further detecting within the spectral emissions atleast one of harmonics and intermodulation distortion (IMD) resultingfrom a second RF signal applied to the load or harmonics; and a controlmodule that varies a parameter of the RF output signal in accordancewith the at least one of the harmonics or the IMD detected in thespectral emissions, wherein the parameter is one of phase, frequency, oramplitude.
 23. The RF generator system of claim 22 wherein the controlmodule adjusts one of a current or a voltage of the RF output signal tovary a width of an ion energy distribution (IED) or a phase of the RFsignal to vary a peak of the IED.
 24. The RF generator system of claim22 wherein the load is an inductively coupled plasma (ICP) system. 25.The RF generator system of claim 24 wherein, the control module variesthe RF output signal in accordance with a selected harmonic detected inthe spectral emissions.
 26. The RF generator system of claim 25 whereinthe control module varies a current or a voltage of the RF output signalin order to control a width of an ion energy distribution (IED) or aphase of the RF signal to vary a peak of the IED.
 27. The RF generatorsystem of claim 26 wherein the control module varies a current or avoltage in the RF output signal in order to control a width of an ionenergy distribution (IED) or a phase of the RF signal to vary a peak ofthe IED.
 28. The RF generator system of claim 22 wherein the sensor isdisposed in one of at an input to a matching network, at an output of amatching network, or within a RF generator.